The present invention relates to an apparatus for converting optical information into electrical information signal and an information storage element. In addition, the present invention relates to a method for storing information in the information storage element.
One type of apparatus for converting information applied as optical images, into electrical signals, was disclosed in Japanese Laid Open Patent Publication No. 62-139481 as an "Apparatus for converting optical image information into electrical signals". In this conversion apparatus, the optical image information is applied at a signal light receiving surface and is stored in a signal light photo-electrical conversion elements of a photo-electrical conversion portion for signal light.
Then, the information that is stored at each time in each of the signal light photo-electrical conversion elements is read by the scanning of sweep light.
In this manner, the above described conversion apparatus is extremely effective for obtaining electrical signals corresponding to optical information which is stored in each of the areas where the sweep light is irradiated.
In the case of a conventional apparatus for converting optical image information into electrical signals as described above, the scanning by the sweep light is performed either one dimensionally or two dimensionally. The information read is performed by the scanning of the sweep light and so the information read speed is determined by the scan speed of the sweep light. Accordingly, increasing the speed of the information conversion requires that the scan speed of the sweep light be increased but there is a limit as to how fast the sweep speed can be made.
In addition, in the above described prior art reference Japanese Laid Open Patent Publication No. 62-139481, the contents of the information that is held at each time by each of the signal light photo-electrical conversion elements in the photoelectric conversion portion for signal light is read as a continuous time series by irradiating the sweep light to the sweep light receiving surface. Accordingly, the optical image information that is held as an entirety by the photoelectric conversion portion for signal light to which the signal light is irradiated is converted into an electrical signal time series accompanying the scan of the sweep light.
The spatial positions in the photoelectric conversion portion for signal light for the optical image information correspond to the scan positions of the sweep light. The time axis of the time signal electrical signals obtained by the conversion of the optical information corresponds to the scan timing of the sweep light and is determined by the scan speed. Accordingly, if the scan speed of the sweep light is accurately determined, then the spatial positions of the sweep light and the positions on the time axis of the converted electrical signals have a relationship which is linearly proportional.
However, in actuality, it is extremely difficult to scan the light beam accurately and at a predetermined speed. For example, one of the methods of scanning the light beam at a constant speed is by light scanning by a polygonal mirror and an f.theta. lens. In such an optical system, variations in the rotational speed of the motor that rotates the polygonal mirror and aberrations and the like in the manufacture of the polygonal mirror, make it impossible practically, to scan at a constant speed.
In the above described apparatus for converting optical image information into electrical signals, the read accuracy of the information is lowered because the scan speed of the sweep light is not accurate when the optical image information is converted into electrical signals. For example, when the electrical signals obtained from the conversion are used as the basis for the information image, that reproduced image no longer accurately corresponds to the optical image information.
Furthermore, the apparatus that converts the optical information into electrical signals is used as an information storage apparatus. The inventors of the invention of this application have proposed an information storage element of this type in Japanese Laid Open Patent Publication No. 63-34797.
In this type of conventional information storage element, when the information is read, light is irradiated in order to read that information. Then the information storage element has an electrical capacitance C for all of the elements other than those to which the light is irradiated. This electrical capacitance C is relatively large for the above described information storage elements and becomes disadvantageous when the information storage elements have a large area. For example, the above described electrical capacitance C exists for the elements in their entirety and so the electrical capacitance C becomes larger in accordance with the area of those information storage elements. Therefore when this electrical capacitance C becomes larger, there is a delay in the response when the information is stored or read.
In addition, the prior art reference Japanese Laid Open Patent Publication No. 62-139481 discloses an apparatus for converting an optical image into electrical signals. According to the content of the technology disclosed in this prior art reference, the irradiation of the optical signals that include optical image information and their conversion into electrical signals are performed at the same time. This is to say that the information storage performance of the optical image information to electrical signal conversion element is not considered. However, this does not means that there is no information storage performance for these elements as these optical image information to electrical signal conversion elements have a storage performance for extremely short time intervals in the msec order, for example. Accordingly, the optical image information to electrical signal conversion element can be used as a temporary memory. The optical image information to electrical signal conversion element can also be termed an information storage element. When the above described optical image information to electrical signal conversion element is thought of as an information storage element, there is a problem due to the presence of the above described electrical capacitance C.
Moreover, in the information storage element disclosed in Japanese Laid Open Patent Publication No. 63-34797, it is possible to have information read whenever required. However, when new information is stored with respect to information storage elements that are already storing information, and using the information storage method disclosed in Japanese Laid Open Patent Publication No. 63-34797, it is necessary to have procedures for the prior erasure of the information that has already been stored. Therefore, it is necessary to return the information storage elements back to the initial status where there is no information stored.